This invention relates to digital demodulation systems, and more particularly to an interface device between a plurality of analog signals and a digital computer.
A single point digital demodulation has many advantages including cost, size, power consumption, response time, and error reductions when compared with conventional analog electronic circuit demodulation techniques. The standard method of interfacing alternating signals to digital computers involves the use of an analog demodulator, for each of the input signals, so that the computer can select the read time via the analog-to-digital converter and multiplexer circuitry. The present invention employs a relatively small amount of timing circuitry to synchronize the sampling of the analog signal with its reference, thereby eliminating the need for extra demodulation. This new single point digital demodulation technique can be compared with the standard analog circuitry demodulation technique for six channels of input data as in a gimballed inertial system application. The cost of the new method is 39 dollars to implement compared to a cost of 144 dollars for the standard technique, thus representing a cost savings of almost 75 percent. The size of the new circuit would occupy only one-half of the volume required for the standard demodulation technique.
The conventional method, in addition to requiring extra circuitry, could introduce demodulation errors of up to 10 percent depending on filter criteria and time lags of up to one second depending on bandwidth.
There are many applications that exist for the system of the present invention, both in inertial systems and in other types of computer-controlled devices. It is a practical and useful system for feeding amplitude-modulated periodic signals into a digital computer. Other applications in addition to gimballed inertial systems that could employ this interfacing system include strapdown inertial systems (for the gyro torque rebalance loops), missile radar or optical seeker assemblies, angular measurement devices, and automatic test equipment interfaces.